Modern conversion processes, namely LD (BOF), LD-AC, KALDO etc, which use oxygen blowing from above, as well as those in which the oxygen is fed from below, namely OBM (Q BOP), LWS, etc, have limitations in respect of the efficiency of the desulphurization and dephosphorization reactions. These limitations, which only permit poor elimination of sulphur and of phosphorus from the metal bath, do not allow one to meet, on the one hand, the requirements of steels with high quality and mechanical requirements, such as toughness, and on the other hand the worsening of the primary materials, above all of the fossil fuels in respect of sulphur and phosphorus content, given that, under the impetus of the present energy crisis, it would be opportune to use those that are available, without too many limitations.
A recent tendency to counterbalance these difficulties has caused one to introduce treatment upstream and downstream of the process of making the steel in the converter, that is new processes which are inserted in the metallurgical cycle and which permit the formation of products of higher quality. Only in a few cases has one been able to use such treatments also to permit the advantages of providing less valued fossil fuels.
The treatments carried out on the liquid iron in general permit the sulphur content to be reduced, but only more recently are being put into practice other treatments which permit the phosphorus content to be reduced.
Treatments carried out downstream, that is on the steel, in general have other purposes such as deoxidization, degasing, etc, but can also allow sulphur inclusions to be formed into globules and also the further lowering of the sulphur content and sometimes also of the phosphorus content.
It is evident that increasing the number of fundamental process also increases the complexity of the production cycle and in general the cost of steel making.